Earth Science, Geologic Time & Fossils, PHY-RAI
Planet Earth has billions of years of history, from the time when it was an inhospitable ball of hot magma to when its surface stabilized into a variety of diverse zones capable of supporting many life-forms. Many are the species that lived through the various geologic eras and left a trace of their existence in the fossils that we study today. But Earth is never done settling, as we can see from the earthquakes, tsunamis, volcanic eruptions, and other phenomena manifested in Earth’s crust, oceans, and atmosphere.
Earth Science, Geologic Time & Fossils Encyclopedia Articles By Title
phyllosilicate
phyllosilicate, compound with a structure in which silicate tetrahedrons (each consisting of a central silicon......
physical geology
physical geology, scientific discipline that is concerned with all aspects of the Earth’s structure, composition,......
phytosaur
phytosaur, heavily armoured semiaquatic reptiles found as fossils from the Late Triassic Period (about 229 million......
Piccard, Bertrand
Bertrand Piccard is a Swiss aviator who on March 20, 1999, with copilot Brian Jones, completed the first nonstop......
pickeringite
pickeringite, magnesium-rich variety of the mineral halotrichite MgAl2(So4)4·22Η2Ο...
picrite
picrite, intrusive igneous rock of ultramafic (very silica-poor) composition that is composed largely of olivine......
Pierre Shale
Pierre Shale, division of Upper Cretaceous rocks in the United States (the Cretaceous Period lasted from about......
Piltdown man
Piltdown man, (Eoanthropus dawsoni), a proposed species of extinct hominins (members of the human lineage) that......
Pirsson, Louis Valentine
Louis Valentine Pirsson was a geologist whose studies of the igneous rocks of Montana revealed many previously......
pisolite
pisolite, spheroidal crystalline particle larger than 2 millimetres in diameter (see...
pitchstone
pitchstone, a volcanic glass with a conchoidal fracture (like glass), a resinous lustre, and a variable composition.......
placoderm
placoderm, any member of an extinct group (Placodermi) of primitive jawed fishes known only from fossil remains.......
Planet
Planet, (from Greek planētes, “wanderers”), broadly, any relatively large natural body that revolves in an orbit......
Planetary boundary layer
Planetary boundary layer (PBL), the region of the lower troposphere where Earth’s surface strongly influences temperature,......
Planosol
Planosol, one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO).......
Plasmapause
Plasmapause, portion of the magnetosphere that rotates with the Earth at about four Earth radii (approximately......
plate tectonics
plate tectonics, theory dealing with the dynamics of Earth’s outer shell—the lithosphere—that revolutionized Earth......
- Introduction
- Earth's Layers, Crust, Mantle
- Seafloor Spreading, Continental Drift, Subduction
- Island Arcs, Subduction, Volcanism
- Transform Faults, Continental Drift, Subduction
- Development, Theory, Earth
- Continental Drift, Subduction, Earthquakes
- Hess's Model, Seafloor Spreading, Continental Drift
- Continental Drift, Subduction, Earthquakes
- Seismic Tomography, Earth's Crust, Subduction
- Continental Drift, Subduction, Earthquakes
- Continental Reconstructions
- Extinction, Continental Drift, Subduction
platinum
platinum (Pt), chemical element, the best known and most widely used of the six platinum group metals of Groups......
Platyceras
Platyceras, genus of extinct gastropods (snails) that occurs as fossils in rocks of Silurian to Permian age (about......
Platycrinites
Platycrinites, genus of extinct crinoids, or sea lilies, especially characteristic as fossils of Early Carboniferous......
Platystrophia
Platystrophia, genus of extinct brachiopods (lamp shells) occurring as fossils in marine rocks of the Middle Ordovician......
Playfair, John
John Playfair was a Scottish geologist and mathematician known for his explanation and expansion of ideas on uniformitarianism—the......
Plectoceras
Plectoceras, extinct genus of small marine nautiloid cephalopods, forms related to the modern pearly nautilus,......
pleochroic halo
pleochroic halo, ring of colour produced around a radioactive impurity included in a mineral by alpha particles......
plesiosaur
plesiosaur, (clade Plesiosauria), any of a group of long-necked marine reptiles found as fossils from the late......
Pleuromeia
Pleuromeia, genus of extinct lycopsid plants from the Triassic Period (about 251 million to 200 million years ago)......
Plinthosol
Plinthosol, one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO).......
Pliohippus
Pliohippus, extinct genus of horses that inhabited North America during the Pliocene Epoch (5.3–2.6 million years......
pliosaur
pliosaur, a group of large carnivorous marine reptiles characterized by massive heads, short necks, and streamlined......
plumbojarosite
plumbojarosite, a widespread iron and lead sulfate mineral, PbFe6(So4)4(OH)12, that has been found in the oxidized......
pluton
pluton, body of intrusive igneous rock the size, composition, shape, or exact type of which is in doubt; when such......
Plymouth Rock
Plymouth Rock, granite slab upon which, according to tradition, the Pilgrim Fathers stepped first after disembarking......
Podzol
Podzol, one of the 30 soil groups in the classification system of the Food and Agriculture Organization (FAO).......
podzolic soil
podzolic soil, soil usually forming in a broadleaf forest and characterized by moderate leaching, which produces......
Polar air mass
Polar air mass, air mass that forms over land or water in the higher latitudes. See air mass;...
Polar anticyclone
Polar anticyclone, wind system associated with a region in which high atmospheric pressure develops over or in......
Polar front
Polar front, in meteorology, the transition region separating warmer tropical air from colder polar air in the......
polar region
polar region, area around the North Pole or the South Pole. The northern polar region consists mainly of floating......
polar vortex
polar vortex, large area of persistent low pressure generally located above each of Earth’s polar regions and containing......
polar wandering
polar wandering, the migration of the magnetic poles over Earth’s surface through geologic time. The study of polar......
Poldervaart, Arie
Arie Poldervaart was a U.S. geologist and petrologist, noted for his work concerning crustal evolution and the......
polybasite
polybasite, heavy, black sulfosalt mineral, a sulfide of the elements silver, copper, and antimony ([Ag, Cu]16Sb2S11),......
Polychaete hypothesis
Polychaete hypothesis, theory that conodonts (minute toothlike structures found as fossils in marine rocks) are......
polygnathiform
polygnathiform, conodont, or small toothlike fossil of uncertain relationship found widely in ancient marine rocks,......
polyhalite
polyhalite, a sulfate mineral in evaporite deposits [K2Ca2Mg(SO4)4·2H2O] that often occurs with anhydrite and halite.......
Post, Wiley
Wiley Post was one of the most colorful figures of the early years of American aviation, who set many records,......
potassium nitrate
potassium nitrate (KNO3), an ionic white crystalline salt made up of potassium ions and nitrate ions. Uses of potassium......
Powell, John Wesley
John Wesley Powell was an American explorer, geologist, and ethnologist, best known for his exploration of the......
powellite
powellite, the mineral calcium molybdate, CaMoO4, ordinarily found only as a component of solid solutions in the......
Prasopora
Prasopora, extinct genus of bryozoans, small colonial animals that formed mosslike or encrusting growths, especially......
Precambrian
Precambrian, period of time extending from about 4.6 billion years ago (the point at which Earth began to form)......
Precipitation
Precipitation, all liquid and solid water particles that fall from clouds and reach the ground. These particles......
prefern
prefern, any of a group of extinct plants considered transitional between the first land plants, the psilophytes,......
prehnite
prehnite, pale green to gray, glassy silicate mineral that commonly lines cavities in igneous rocks. It also occurs......
priceite
priceite, an earthy, white borate mineral, hydrated calcium borate (Ca4B10O19·7H2O). It has been found as masses......
Priestley, Joseph
Joseph Priestley was an English clergyman, political theorist, and physical scientist whose work contributed to......
primary mineral
primary mineral, in an igneous rock, any mineral that formed during the original solidification (crystallization)......
proconodontid
proconodontid, a small toothlike structure found in marine rocks formed over a long span of geologic time, that......
Proterozoic Eon
Proterozoic Eon, the younger of the two divisions of Precambrian time, the older being the Archean Eon. The Proterozoic......
Protonosphere
Protonosphere, region in the Earth’s upper atmosphere where atomic hydrogen and protons (ionic hydrogen) are the......
Proudman, Joseph
Joseph Proudman was a British oceanographer known for his contribution to the Taylor–Proudman theorem of the dynamics......
proustite
proustite, a sulfosalt mineral, silver arsenic sulfide (Ag3AsS3), that is an important source of silver. Sometimes......
pseudomorph
pseudomorph, mineral formed by chemical or structural change of another substance, though retaining its original......
Pseudoschwagerina
Pseudoschwagerina, extinct genus of fusulinid foraminiferans (single-celled animals with hard shells preservable......
Psychrometer
Psychrometer, a type of hygrometer that measures humidity by comparing temperature readings on two similar thermometers.......
Pteranodon
Pteranodon, (genus Pteranodon), flying reptile (pterosaur) found as fossils in North American deposits dating from......
Pteraspis
Pteraspis, genus of extinct jawless fishlike vertebrates found as fossils in Early Devonian rocks (those 398 million......
pterodactyl
pterodactyl, informal term for a subgroup of flying reptiles (Pterosauria) known from the Late Jurassic through......
pterosaur
pterosaur, any of the flying reptiles that flourished during all periods (Triassic, Jurassic, and Cretaceous) of......
Ptilodus
Ptilodus, extinct genus of mammals found as fossils in deposits dated to the Paleocene Epoch (65.5–55.8 million......
Ptolemy
Ptolemy was an Egyptian astronomer, mathematician, and geographer of Greek descent who flourished in Alexandria......
pumice
pumice, a very porous, frothlike volcanic glass that has long been used as an abrasive in cleaning, polishing,......
Pumpelly, Raphael W.
Raphael W. Pumpelly was an American geologist and scientific explorer known for his studies and explorations of......
Purbeck Beds
Purbeck Beds, unit of sedimentary rocks exposed in southern England that spans the boundary between the Jurassic......
pycnocline
pycnocline, in oceanography, boundary separating two liquid layers of different densities. In oceans a large density......
Pycnodontiformes
Pycnodontiformes, order of extinct fishes of the class Actinopterygii, containing the genus Pycnodus, common in......
pyrargyrite
pyrargyrite, a sulfosalt mineral, a silver antimony sulfide (Ag3SbS3), that is an important source of silver, sometimes......
pyrite
pyrite, a naturally occurring iron disulfide mineral. The name comes from the Greek word pyr, “fire,” because pyrite......
pyrochlore
pyrochlore, a complex oxide mineral [(Na, Ca)2Nb2O6(OH,F)] composed of niobium, sodium, and calcium that forms......
pyroclastic flow
pyroclastic flow, in a volcanic eruption, a fluidized mixture of hot rock fragments, hot gases, and entrapped air......
pyroelectricity
pyroelectricity, development of opposite electrical charges on different parts of a crystal that is subjected to......
pyrolite
pyrolite, rock consisting of about three parts peridotite and one part basalt. The name was coined to explain the......
pyromorphite
pyromorphite, a phosphate mineral, lead chloride phosphate, [Pb5(PO4)3Cl], that is a minor ore of lead. It occurs......
pyrophyllite
pyrophyllite, very soft, pale-coloured silicate mineral, hydrated aluminum silicate, Al2(OH)2 Si4O10, that is the......
pyroxene
pyroxene, any of a group of important rock-forming silicate minerals of variable composition, among which calcium-,......
pyroxenite
pyroxenite, dark-coloured, intrusive igneous rock that consists chiefly of pyroxene. Pyroxenites are not abundant;......
pyrrhotite
pyrrhotite, iron sulfide mineral (Fe1–xS) in the niccolite group; in it, the ratio of iron to sulfur atoms is variable......
Pääbo, Svante
Svante Pääbo is a Swedish evolutionary geneticist who specialized in the study of DNA from ancient specimens and......
Qafzeh
Qafzeh, paleoanthropological site south of Nazareth, Israel, where some of the oldest remains of modern humans......
Qinghai earthquake of 2010
Qinghai earthquake of 2010, severe earthquake that occurred on April 14, 2010, in the isolated southern Yushu Tibetan......
quartz monzonite
quartz monzonite, intrusive igneous rock (solidified from a liquid state) that contains plagioclase feldspar, orthoclase......
Quasi-biennial oscillation
Quasi-biennial oscillation, layer of winds that encircle Earth’s lower stratosphere, at altitudes from 20 to 40......
Quaternary
Quaternary, in the geologic history of Earth, a unit of time within the Cenozoic Era, beginning 2,588,000 years......
Quenstedt, Friedrich August
Friedrich August Quenstedt was a German mineralogist and paleontologist. Quenstedt studied at the University of......
Quetzalcoatlus
Quetzalcoatlus, genus made up of two species of giant pterosaurs classified in the family Azhdarchidae, which contains......
quicksand
quicksand, state in which saturated sand loses its supporting capacity and acquires the character of a liquid.......
Radiative forcing
Radiative forcing, a measure, as defined by the Intergovernmental Panel on Climate Change (IPCC), of the influence......
Radiosonde
Radiosonde, balloon-borne instrument for making atmospheric measurements, such as temperature, pressure, and humidity,......
Rain
Rain, precipitation of liquid water drops with diameters greater than 0.5 mm (0.02 inch). When the drops are smaller,......
rainbow
rainbow, series of concentric coloured arcs that may be seen when light from a distant source—most commonly the......